Product-of-coefficients indirect effect with the Sobel standard error
Source:R/causal_native.R
morie_indirect_effect_sobel.Rd\(IE = ab\) with \(s_{ab} = \sqrt{b^2 s_a^2 + a^2 s_b^2}\). Reported because it is what this quantity is classically paired with, but the product of two normals is not normal and is skewed when both coefficients are near zero, so the test is conservative exactly where mediation is most in doubt; a bootstrap is the better instrument there. Without both standard errors the test is skipped rather than faked.